Reddit reviews Valterra A01-0187VP Flexible Tank Wand, Gray

For the ice in the tank solutions, I'd look at this before spending any time with that method.

I have one of these, and use it occasionally to flush the tank (but the sensor has shown full for years). If you have the type of setup where you can see into the tank from the toilet, there are some straight ones that might do a better job.

My basic method is to close the tank, with that wand down the toilet, and let if fill / drain repeatedly until it runs clear. I rotate it several times while filling to get the corners. We have a laundry room where I hook a short hose up for the flush, but if I didn't I'd probably just put a tee / connection in the toilet water supply.

I've used this http://amzn.to/2qSvB9L both for the toilet itself and for the roof vents (when the caps were off).